nuclear chemistry ch. 28. nuclear radiation 28-1

Download Nuclear Chemistry Ch. 28. Nuclear Radiation 28-1

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  • Nuclear ChemistryCh. 28

  • Nuclear Radiation28-1

  • RadioactivityRadioactivity = spontaneous emission of radiation by an unstable atomic nucleus.Some elements give off radiation naturally, without an input of energy!!In chemical reactions the number of electrons changes, in nuclear reactions the number of protons + neutrons changes!If the proton number changes a new element is made!

  • 6Nuclear NotationNuclear Notation Indicates mass number and atomic number, allowing isotopes to be differentiated23892U can also be written as Uranium-238Superscript: Mass # = # of protons plus neutronsSubscript: Atomic # = # of protonsIsotopes have same # of protons but different # of neutrons

  • Ex: Isotopes of Hydrogen

  • Radioactive DecayRadioactive Decay = release of radiation by radioactive isotopes, or radioisotopes, to become more stable.Nuclei of radioisotopes are unstable, give off varying degrees and different types of nuclear radiation.Three types of nuclear radiation:1) Alpha particles 2) Beta particles3) Gamma rays

  • Alpha DecayAlpha particle: helium nuclei consisting of 2 protons and 2 neutrons (+2 charge!)Symbol: 42He or Affect: large in size, do not penetrate into matter easily, stopped by thin layer of material (paper, skin)Alpha decay: nucleus releases an alpha particle, becoming a different elementDecreases mass of original nucleus by 4 and the new element has an atomic number 2 less than original

  • As uranium decays it becomes multiple elements releasing multiple types of radiation!Transmutation = when a nucleus releases either an alpha or beta particle the atomic # changes becoming a different element!

  • Beta DecayBeta particle = a high energy electron with a charge of -1.Symbol: 0-1e or -Affect: smaller, lighter, can be stopped only by thicker materials (aluminum foil or wood).Beta decay = decaying nucleus turns into new element with atomic number + 1 but with same mass.

  • Gamma DecayGamma ray = high energy form of electromagnetic radiation without mass or charge.Symbol: or 00Affect: Very hard to stop, only thick layers of lead or thick concrete. Causes great harm to living cells Gamma Decay = only energy is given off, usually occurs simultaneously with other types of decay, often omitted from equations.

  • OverviewDraw!

    Type of RadiationSymbolAtomic massAtomic #AffectAlphaBetaGamma

  • Type of RadiationSymbolAtomic massAtomic #AffectAlpha42He Decrease by 4Decrease by 2Stopped by thin layerBeta0-1e -sameAdd 1Stopped by thick materialGamma00samesameOnly stopped by thick concrete, or lead

  • Explain why the 3 types of radiation moved in the following directions!

  • Nuclear Transformations28-2

  • Radioactive DatingUnlike chemical reactions affected by temperature, pressure, and concentration, the rate of nuclear decay cannot be changed!Able to predict amount of decay that has occurred.Half-life = time it takes for half the given amount of a radioisotope to decay.

    Is that what atoms do when theyre single?!

  • Half-life Calculation:MO = 2xMrWhere MO = original mass, x = # of half-lives, Mr = mass remainingExample: 2.00 g of nitrogen-13 emits beta radiation with a half-life of 10 minutes. Write a nuclear equation.137N 138O + 0-1eHow long is 3 half-lives?10 minutes x 3 half-lives = 30 minutesHow many grams of oxygen-13 will be present at the end of 3 half-lives?MO = 2xMr 2.00g = 23Mr Mr = 0.250g of oxygen-13

  • What is the half-life (time) of this radioactive sample?

  • Commonly used Radioisotopes for Radioactive DatingCarbon-14 used to date artifacts made of organic materialUranium-238 used to date rocks as old as solar systemRadon-222 and Thorium-234 used in nuclear medicine

    IsotopeHalf-lifeRadiation emittedCarbon-145.73 x 103 yearsUranium-2384.46 x 109 yearsRadon-2223.8 days

  • Nuclear Reactions and Energy28-3

  • Nuclear FissionNuclear Fission = an atomic nucleus is split into two or more large fragmentsEx: Uranium is bombarded with a neutron forming two lighter elements: krypton and barium, 3 neutrons, and a large amount of energy!23592U + 10n 14056Ba + 9336Kr + 310nIf the reaction takes place too quickly an explosion will occur (atom bomb), if it is controlled to release heat slowly it can be used to heat water and do other useful work! = nuclear reactor

  • San Onofre Nuclear Power Plant(Fission of Uranium!)

  • Nuclear Fission as a source of energy!Pros: >100 nuclear reactors in U.S.Provide ~20% of electricity usedDo not release pollutants to air

    Cons:Form highly radioactive wasteCan cause serious accidentsLimited supply of fissionable materialHigher cost than fossil fuels

  • Nuclear AccidentsChernobyl, Ukraine, 1986Fukushima, Japan, 2011

  • Nuclear FusionNuclear Fusion = two or more nuclei combine to form a larger nucleus.Fusion is the process that produces energy in stars, sun (2 H nuclei form He)21H + 31H 42He + 10ndeuterium + tritium helium + neutronThe fusion of hydrogen produces 20 times the energy produced by fission of uranium but can only take place at very high temperatures! (40 million C)

  • Nuclear Fusion as a source of energy!Pros:Fusion done successfully in laboratoriesDeuterium, a fuel in fusion, abundant on EarthNo radioactive products producedEasier to control than fissionCons:Requires large input of energy, 200 million K heat required!!!Only known source of this amount of thermal energy is an atom bomb, thus must be used to start reaction!Material to contain reaction meltsTokamak = uses electromagnets to contain nuclei, radio waves initiate fusion, but no net energy produced

  • The Large Hadron Colliderat CERN, Switzerland17 mile circumference, 574 ft below the surface.Worlds largest particle accelerator

  • Artificial Transmutation: can occur by applying an outside force.Requires lots of energy!! High speed neutrons act as bullets to hit nuclei = Particle accelerators Neptunium and Plutonium were discovered in lab (synthetic elements), as were all elements with atomic #s greater than 92 on periodic table = transuranium elements.

    Fermilab, Illinois Shutdown in 2011

  • Comparison (DRAW!)